Ferrule With Relief To Reduce Galling

ABSTRACT

High localized loading, galling, and high torque forces have been generally eliminated or greatly reduced in a two ferrule tube fitting assembly through suitable modification of the rear ferrule so as to redirect the reaction forces acting between the front ferrule and the drive nut. The rear ferrule has a cylindrical interior wall that closely surrounds the tube end and is provided on the interior cylindrical wall with a circumferentially continuous radial recess that is located between the nose and rear wall of the rear ferrule. The rear ferrule also has a radially external wall that is substantially conical and additionally shaped to extend radially outward toward the enlarged diameter portion or flange of the rear ferrule. The rear ferrule further includes a contoured face on the rear driven surface of the ferrule that engages the drive surface of the drive nut.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/374,026, filed on Feb. 25, 2003 for FERRULE WITH RELIEF TOREDUCE GALLING, which is a continuation of U.S. patent application Ser.No. 09/469,549 filed on Dec. 12, 1999 for FERRULE WITH RELIEF TO REDUCEGALLING, now U.S. Pat. No. 6,629,708, which is a continuation-in-part ofU.S. patent application Ser. No. 09/054,186 filed on Apr. 2, 1998, nowU.S. Pat. No. 6,131,963, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/834,255 filed on Apr. 15, 1997, now U.S. Pat.No. 5,882,050, the entire disclosures of which are fully incorporatedherein by reference.

BACKGROUND OF INVENTION

[0002] The subject invention is directed to the art of ferrule type tubefittings. More particularly, the invention concerns a two ferrulefitting wherein the rear ferrule is designed to reduce the torquerequired to rotate the associated nut and to also reduce galling betweenthe rear ferrule and the interior surface of the drive nut. Theinvention may also be applied in a single ferrule fitting.

[0003] A commercially available and highly successful two ferrulefitting used for tubing is illustrated in FIGS. 1 and 1A. FIG. 1 showsthe fitting components in a finger tight position preparatory to finaltightening, whereas FIG. 1A shows the fitting after final tightening. Asshown, the fitting comprises a body 10 having a cylindrical opening 12counterbored for receiving tube end 13. A tapered, frusto-conicalcamming mouth 14 is located at the axial outer end of the counterbore. Afront ferrule 16 having a smooth, cylindrical inner wall 18 is closelyreceived on the tube. The front ferrule has a frusto-conical outersurface 20 to be received in the camming mouth.

[0004] Associated with the front ferrule 16 and located axially outwardtherefrom is a rear ferrule 22 configured as shown with a tapered noseportion 24 and a rear flange 26 having an inclined end surface 28. Theinclined end surface of the rear ferrule 22 provides a radial componentas well as an axial component of the pull-up forces acting on the endsurface as will be apparent to those skilled in the art. The taperednose 24 enters a tapered camming surface in the rear surface of thefront ferrule.

[0005] The ferrules 16, 22 are enclosed by a drive nut member 30threaded to the body 10. During tightening and make-up of the fitting,the inner end face, flange, or shoulder 32 of the nut acts against theinclined end surface 28 of the rear ferrule to drive the ferrulesforwardly into the fully engaged position shown in FIG. 1A.

[0006] The small diameter portion or nose of the rear ferrule isdimensioned so that it plastically deforms during make-up of thefitting. This action is desirable since it results in tight grippingengagement of the outer wall of the tubing. The thickness of the noseportion cannot be reduced to an extent that the rear ferrule deforms toomuch and only the rear ferrule adequately grips the outer wall of thetubing. That is, the two ferrule assembly requires desired deformationof both the front and rear ferrules for the gripping and sealingcapabilities that have made this two ferrule assembly a commerciallysuccessful product. On the other hand, the thickness of the nose of therear ferrule cannot be enlarged to such an extent that it results in astructural arrangement that is too stiff and does not permit the desiredrear ferrule deformation.

[0007] A more complete description and understanding of the conventionaltwo ferrule phase controlled sequential gripping action resulting fromthe inclined rear surface and the interaction of the front and rearferrules is set forth in U.S. Pat. No. 3,103,373 issued to Lennon, etal., the entire disclosure of which is fully incorporated herein byreference.

[0008] Accordingly, it will be recognized by those skilled in the artthat a predetermined wall thickness of the nose of the rear ferrule isdesired that achieves the desired gripping of the tube and cooperateswith the front ferrule in such a manner that it achieves its desiredgoals of gripping and sealing the tube.

[0009] It is also recognized that operators of fluid systems test thesystem prior to a production run by pressurizing the system to anappropriate factor times the rated system pressure. In this manner, theoperator can easily detect whether the fluid system is sealed, i.e. thatthere are no leaks. With this knowledge, the manufacturer can provide afitting in which the nose of the rear ferrule will not have anyadditional plastic deformation at the elevated test pressure.Accordingly, the elevated test pressure is used to determine the desiredwall thickness of the nose portion of the rear ferrule to achieve thedesired amount of deformation of the nose and permit the front and rearferrules to properly grip and seal with the outer wall of the tube.

[0010] It has also been found that galling of the drive nut sometimesoccurs in the drive face area of engagement between the inner end faceof the drive nut and the rear wall of the rear ferrule. After analysis,it is believed that the axial thrust or pull-up force between the frontand rear ferrule is essentially parallel to the axis of the fitting.This axial thrust causes the rear corner region of the rear ferrule toselectively concentrate pull-up stress at the inside drive surface ofthe nut particularly in a localized area to produce the galling. Thisalso noticeably increases the nut torque forces experienced duringmake-up even if galling is absent. Accordingly, it would be highlydesirable to provide a design wherein the thrust forces do not producethe high localized loading with the resultant galling and high torqueforces.

SUMMARY OF INVENTION

[0011] In accordance with one embodiment of the invention, a tubefitting includes a fitting body having a cylindrical bore for receivinga tube end and including a tapered mouth at one end of the bore; a drivemember having a threaded engagement with the body and having a ferruledrive surface; a first ferrule having a tapered first end that extendsinto the tapered mouth of the fitting body and having a second end witha tapered recess that axially extends toward the first end; and a secondferrule having a cylindrical interior wall, a tapered first end thatextends into the tapered recess of the first ferrule, and having acontoured face on a second end thereof that engages the drive memberferrule drive surface; the second ferrule interior wall having acircumferential recess located between the first and second ends of thesecond ferrule; the recess and the contoured face reducing stressconcentrations on the drive member drive surface when the fitting ismade up.

[0012] Another aspect of the invention includes forming the rear ferrulewith a cylindrical interior wall that has a first diameter at theforward or nose end of the ferrule and a second diameter at the rear endof the ferrule wherein the second diameter is greater than the firstdiameter so that, for example, a single tool can be use to form thecircumferential recess and the cylindrical wall. Still a further aspectof the invention includes forming a notch on the outside diameter of theferrule body that joins the second ferrule first and second ends. Inanother aspect of the invention, a contoured drive surface is providedon the drive member rather than on the rear ferrule second end. Thepresent invention may also be practiced with ferrules that are made ofharder base metal than prior ferrules. The invention may also bepracticed with ferrules that have been case hardened either entirely orselectively on the ferrule surface. In general, the present inventionmay be used in single ferrule fittings as well.

[0013] These and other aspects and advantages of the present inventionwill be apparent to those skilled in the art from the followingdescription of the preferred embodiments in view of the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The invention may take physical form in certain parts andarrangements of parts, preferred embodiments and a method of which willbe described in detail in this specification and illustrated in theaccompanying drawings which form a part hereof, and wherein:

[0015]FIG. 1 is a longitudinal cross-sectional view of a well knownprior art two ferrule swage-type fitting;

[0016]FIG. 1A is an enlarged view of the circled area of FIG. 1 showingthe prior art fitting in a made condition;

[0017]FIG. 2 is a view like FIG. 1 but showing a preferred embodiment ofa fitting incorporating a modified rear ferrule designed to improvereaction force transmission through the rear ferrule;

[0018]FIG. 3 is a greatly enlarged showing of the circled area of FIG.2;

[0019]FIG. 4 is a detailed, partial cross-sectional view of a preferredform of rear ferrule;

[0020]FIG. 5 is a cross-sectional view similar to FIG. 4 showing asecond preferred form for the rear ferrule;

[0021]FIG. 6 is a cross-sectional view of the fitting of FIG. 1particularly showing the rear ferrule positioned between the frontferrule and the nut at initial make-up (graphically meshed for finiteelement analysis);

[0022]FIG. 7 is a view of the fitting of FIG. 6 in a made-up conditionand illustrating the stress concentrations;

[0023]FIG. 8 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

[0024]FIG. 9 is a view of the fitting of FIG. 8 in a made-up conditionand illustrating the stress concentrations;

[0025]FIG. 10 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

[0026]FIG. 11 is a view of the fitting of FIG. 10 in a made-up conditionand illustrating the stress concentrations;

[0027]FIG. 12 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

[0028]FIG. 13 is a view of the fitting of FIG. 12 in a made-up conditionand illustrating the stress concentrations;

[0029]FIG. 14 is a table of different geometrical variations of the rearferrule configuration;

[0030]FIG. 15 is a cross-sectional view of an alternative embodiment ofa two ferrule fitting;

[0031]FIG. 16 is an enlarged view of the ferrule region of theembodiment of FIG. 15;

[0032]FIG. 17 is a partial view of a rear ferrule with a contoured facein accordance with one aspect of the invention;

[0033]FIG. 18 is a partial view of a contoured rear ferrule shown in theengaged position with a front ferrule and drive nut surfaces prior topull up;

[0034]FIG. 19 is a view of the embodiment of FIG. 18 in the pulled upcondition showing stress distributions;

[0035]FIG. 20 is another embodiment of the invention;

[0036]FIG. 21 illustrates stress distributions in a two ferrule fittingthat does not use a contoured rear ferrule;

[0037]FIG. 22 illustrates another embodiment of a rear ferrule designincorporating a circumferential recess;

[0038] FIGS. 23A-F illustrate various alternative rear ferrule drivensurface profiles;

[0039] FIGS. 24A-G illustrates an alternative embodiment of theinvention wherein the drive surface of the nut is provided with acontour surface;

[0040]FIG. 25 illustrates another alternative embodiment of a ferrulehaving an inner cylindrical bore formed of two different diameters;

[0041]FIG. 26 illustrates another alternative embodiment of a ferrulehaving an outer notch or recess in the ferrule body;

[0042]FIG. 27 illustrates another alternative embodiment of theinvention of a ferrule having a notched inner bore, a contoured rearsurface, an outer notch and a crown portion on the ferrule nose region;and

[0043]FIG. 28 is a finite element analysis illustrating one aspect ofthe invention of a high friction tube grip area axially spaced from astress riser created at the nose of the ferrule.

DETAILED DESCRIPTION

[0044] Referring now to the drawings wherein the showings are for thepurposes of illustrating preferred embodiments of the invention only andnot for purposes of limiting same, FIG. 2 illustrate the overallarrangement of a fitting incorporating the invention. It should be notedthat in many of the illustrations herein of the ferrule profiles, theferrules are shown in partial cross-section for clarity and ease ofunderstanding, particularly for views of the ferrule geometry andprofile wherein it is only necessary to illustrate a portion of theentire ferrule in sectional view. The FIG. 2 embodiment has the majorcomponents identified with the same reference numerals used with respectto the description of the prior art device of FIGS. 1 and 1A. Adescription of a FIG. 1 element is to be taken as equally applicable tothe FIG. 2 elements that are correspondingly numbered unless otherwisenoted. In particular, in the FIG. 2 embodiment, the rear ferrule 22′ hasbeen modified in a manner to cause the reaction forces acting betweenthe front ferrule through the rear ferrule to the nut to have asignificant force component that is directed radially outward. This isin contradistinction to the FIGS. 1 and 1A embodiment wherein the forcecomponent under consideration has a high axial component. Specifically,as shown in FIG. 4, force component A extends generally axially of therear ferrule 22′ and results in an increase in the loads applied at theradial inner face of the rear ferrule driven surface 28′ and nutshoulder 32′. As previously discussed, high localized loading or stressconcentration in this area produces high torque and galling.

[0045] While the invention is described herein with particular referenceto a two ferrule system, such explanation is exemplary in nature andshould not be construed in a limiting sense. Various aspects of thepresent invention may also find application in a single ferrule fitting.

[0046] In one embodiment of the invention, a redirection of the reactionforces is achieved by providing a circumferential recess 40 throughoutthe inner surface of rear ferrule 22′. Note that circumferential recess40 is located generally midway between the opposite ends of rear ferrule22′ and this results in the inner surface of the rear ferrule beingreduced to two relatively axially narrow substantially cylindrical andcontinuous contact areas 42 and 44. By so modifying the rear ferrule,the forces which are conducted from the front ferrule through the rearferrule to the nut shoulder 32′ tend to be directed more radiallyoutward such as diagrammatically illustrated by the force line B of FIG.4.

[0047] In this embodiment, the generally flat contact areas 42 and 44have substantially the same diameter; however in an alternativeembodiment, these two regions may have different diameters, for exampleit may be desirable in some applications to have the diameter of therear flat contact area 42 slightly greater than the diameter of theforward flat contact area 44, for example, by a few thousandths, morepreferably one to three thousandths of an inch. In yet a furtheralternative embodiment, the rear flat contact area 42 may be eliminatedas a contact area by providing a counterbore in this area. Particularlyfor larger ferrule sizes, the single flat in the nose section of therear ferrule may be sufficient to maintain proper ferrule alignment onthe tubing during installation. These alternatives will be more fullydescribed hereinafter.

[0048] Another important feature of the invention is best exemplified bycomparing the rear ferrule 22 of FIG. 1 with the rear ferrule 22″ of theFIG. 2 embodiment. Particularly, the outer radial wall 50 of the rearferrule 22″ includes a conical section that increases in radialdimension as it extends from the forward nose portion 52, that isreceived in the rear chamfer region 53 of the front ferrule, to the rearflange 26″. In the prior art arrangement (FIGS. 1 and 1A), the rearferrule has a cylindrical through bore and an outer radial wall thatextends parallel to the inner surface defining the through bore in thisregion. In other words, the rear ferrule has a constant annular wallthickness t. In the embodiment of FIG. 2 the outer wall has the conicalor tapered configuration that provides sufficient wall thickness t andcontrolled deformation of the nose portion when the recess isincorporated into the modified rear ferrule. Preferably, the outer wall50 has a generally uniform angle or taper as it extends between thereduced dimension of forward nose portion 52 received in the cammingmouth of the front ferrule and the enlarged diameter of rear flange 26″.Again, this provides controlled deformation of the rear ferrule so thatforward nose portion 52 is plastically deformed radially inward alongforward contact area 44 into gripping, sealed engagement with the outerwall of the tube. Note that in FIG. 4 the recess 40 is so shaped as toappear that the dimension t is constant, though it need not be. Forexample, if the recess 40 is formed such as in many of the illustrationsof FIGS. 14, 17 and 18, the tapered outer wall 50 provides a non-uniformthickness t between forward nose portion 52 and rear flange 26″.

[0049] The wall thickness “t” and the geometry and configuration of therear ferrule 22′ are selected for a particular application in order tobalance and properly align rear ferrule 22′ on the tubing and to assurethat the rear ferrule 22′ cooperates with the front ferrule 16′ toachieve the desired phase controlled sequential gripping operationduring pull-up to assure a proper seal on the tubing. During fittingpull-up, the rear ferrule 22′ applies a vector force against the outersurface of the tube end 13 that has both axial and radial components.The radial component force enables an axial friction force on the tubesurface to achieve excellent gripping and sealing action. This axialfriction force balances against an axial tube grip reaction force fromthe tube end 13.

[0050] The combined geometry of the tapered outer wall 50 along with therecess 40 cause a ‘hhinge” effect of forward nose portion 52. Theselected geometry and configurations will depend on such factorsincluding but not necessarily limited to the materials used for thefitting components, the tube material and wall thickness, the operatingpressure for the fitting, whether the rear ferrule is to be casehardened or not, and so forth. In order to maintain proper sequentialgripping operation during make-up, it is important that the rear ferrule22′ forward nose portion 52 does not collapse too soon otherwise thefront ferrule 16′ may not have sufficient gripping force on the tubewall or an inadequate seal force between the front ferrule 16′ and thetapered camming mouth 14′. If the rear ferrule 22′ collapses too laterelative to the front ferrule, then the rear ferrule 22′ may not haveadequate gripping force on tube end 13.

[0051] The rear ferrule 22′ hinge effect directs the rear ferruleapplied force at the forward nose portion 52 against the tube wall at asignificant radial vector angle from the tube surface. This ferruleapplied force vector B thus has a significant radial component whileenabling the significant axial friction force. Thus, a smaller axialcomponent force applied via the drive nut member 30′ sufficientlyopposes the axial tube gripping reaction force in contrast to when theapplied force is substantially axial as in the prior art of FIGS. 1 and1A. The rear ferrule 22′ grip of tube end 13 thus approaches atoggle-like hinged action. The smaller axial component force results inreduced drive nut member 30 pull-up torque to achieve the same tubegrip.

[0052] In addition, during fitting pull-up, this hinge characteristicdirects the tube reaction force through the rear ferrule 22′ generallytoward the central region of the rear ferrule driven surface 28, thatcontacts the drive surface of the nut shoulder 32′. This results in thereaction forces being more evenly distributed across the rear ferruledriven surface 28′ to avoid or reduce high concentrations of stress,thus reducing or eliminating galling and reducing pull-up torque withoutloss of tube gripping force. In many cases it may be preferred that thereaction forces be directed in a direction generally normal to rearferrule driven surface 28′. The increased tube gripping force resultingfrom the applied radial force also imparts greater penetration orswaging of the rear ferrule 22′ nose portion 52′ onto tube end 13. Thisprovides an excellent tube grip and seal with lower applied torque, andalso provides greater resistance to vibration fatigue by providing aswaged region of high gripping pressure behind (i.e. axially rearward)of the tube stress riser created at the forward end of the nose of therear ferrule 22. FIG. 28 illustrates this result, in that the stressriser region 400 where the nose penetrates tube end 13 is axiallyforward of a swaged region 402 of high frictional engagement between theferrule nose and the tube end. High frictional area or swage produces acollet effect that secures the ferrule on the tube wall and protects thestress riser region 400 from vibration. Good gripping action of the rearferrule forward flat contacting area 44 of the nose portion onto thetube is important for overall performance of the fitting, in contrast toany contact pressure between the rear ferrule rear flat contacting over42. In many cases, there is no need for a contact between rear contactsarea 42 and tube end 13.

[0053] Another benefit resulting from the reduced galling and lowerpull-up torque of the present invention is that re-make of the fittingis facilitated. BBy “re-make” is simply meant that, in someapplications, the user desires to separate a tube fitting afterinstallation, possibly to replace a valve, tubing or to perform otherroutine maintenance and repair, and then to re-install the same fittingwithout replacing the ferrules and/or nut or body. f the rear ferruleand drive nut have become galled, then the torque required for re-makeof the fitting may be prohibitive or impossible, or the fitting may notadequately re-seal. With the use of the present invention tosignificantly reduce or eliminate galling and reduce pull-up torque,re-make is facilitated.

[0054] Although the present invention is useful with many differentmaterials, it has particular advantages when used with stainless steelfittings and tubing, including but not limited to 316 and 316L stainlesstubing, but includes in addition to other alloys, Hastalloy, Inconel,Monel alloys 400 and 500, 254SMO and steel, and duplex stainless steelsuch as, for example, SAF 2507. The present invention can be used withor without case hardening on all or part of the surfaces of the ferrulesas required.

[0055] With respect to case hardened ferrules or ferrules made ofmaterials substantially harder than 316L stainless steel, the presentinvention allows the fitting 10 to be properly pulled up with thedesired phase controlled sequential gripping of the tube wall. If aconventional ferrule, particularly the rear ferrule, was case hardenedor made of a very hard material, the ferrule would be too stiff toachieve proper seal and grip of the tube wall. The present inventionhowever facilitates the use of ferrules of hard materials or that havebeen case hardened over part or all of their surface. Case hardeningherein refers to the treatment of the ferrules in such a manner as toprovide a carbon or nitrogen rich surface that substantially hardens theferrule body as compared to the underlying base metal, as is known tothose skilled in the art.

[0056]FIG. 5 illustrates another preferred embodiment of the rearferrule in which the recess 40 has is defined by two different angles(an obtuse triangle). For example, the smaller first angle defined withthe inner surface increases as it extends rearwardly from forwardcontact area 44 toward the rear flange 26′. The larger second angle(approximately twice the angular dimension of the first angle) increasesas it extends forwardly from rear contact surface 42 toward the noseregion. These angles thus intersect at an axial position that is locatedbeneath the intersection of the outer wall 50 with the rear flange.Accordingly, the stresses are more evenly distributed over the rearferrule driven surface 28′ Turning to FIGS. 6 and 7, the rear ferrule ofthe prior art arrangement of FIG. 1 is shown before and after make-up ofthe fitting. The fitting was subjected to a finite element analysis, theresults of which are particularly evident in FIG. 7. There, shadedregions in the rear flange of the rear ferrule and the nut evidence theforce and stress concentrations encountered upon make-up of the fitting.Particularly, a region of high stress concentration is designated atregion 60. Regions of progressively decreased stress concentration areidentified by numerals 62, 64, 66, 68, and 70. Thus, the large stressconcentration at the radial inner location of rear ferrule drivensurface 28′ results in increased torque during make-up and potentialgalling of the nut.

[0057]FIGS. 8 and 9 show another modified rear ferrule in accordancewith the teachings of the present invention. This rear ferrule is thesame as shown in FIG. 5. As particularly evident in FIG. 9, the regionof high stress concentration is substantially reduced in size whencompared to FIG. 7. This indicates that the stresses have been moreuniformly dispersed over the rear face of the flange of the rearferrule. Thus, the torque is reduced and the potential for galling islikewise reduced.

[0058]FIGS. 10 and 11 represent the rear ferrule shown and described inFIG. 4. Here, the finite element analysis illustrates that the region ofhigh stress concentration is substantially removed at the rear face anda more uniform distribution of stresses obtained. Again, the torqueforces associated with make-up are thus reduced with the correspondingreduction in localized stress concentrations. The recess and conicalouter wall provide a radial component to the forces generated in thefitting and transferred through the rear ferrule while still providing adesired gripping and sealing of the tube.

[0059] The embodiment of FIGS. 12 and 13 also achieves these sameobjectives. The recess is of a slightly different configuration, i.e.,the recess is more sharply defined in the inner wall of the rearferrule. It is also shifted slightly forwardly so that the deepestportion of the recess is located forwardly of the rear flange. However,the outer wall is still of conical configuration and in conjunction withthe recess distributes the stresses along the rear face of the rearferrule.

[0060] As is apparent with the various embodiments described above, therecess and the tapered outer wall do not require a particularconformation to achieve the stress distribution and reduced torque formake-up of the fitting. In fact, a number of proposed alternativeembodiments are illustrated in table form in FIG. 14. For example, thefirst row of geometries have a standard location that is generallydefined as the rear edge of the recess being located axially beneath theintersection of the outer wall and the enlarged flange. The tear drop,right triangle, rectangle, oval, square circular, obtuse triangle,curve, and compound curve are various shapes that the recess may adopt.Moreover, the recess can be positioned at a forward location (secondrow), or a rearward location where the deepest portion of the recess ispositioned beneath the enlarged flange (third row) while still adoptingthe various configurations. Still further, the orientation of the shapescan be reversed as demonstrated by the various geometries in the fourthrow or the sixth row, or the recess may be defined by multiple recessesas shown in the geometries of the fifth and eighth rows. Alternatively,the recess(es) may be enlarged as indicated in the seventh and eighthrows. Accordingly, the invention is not limited to the particularconfigurations shown and described in the earlier embodiments of FIGS.2-13, but may also be incorporated into selected other geometricalconfigurations.

[0061] With reference to FIGS. 15-20, another embodiment of theinvention is illustrated. As noted herein above, the use of a recess 40in the rear ferrule 22′ significantly reduces stress concentrations atshoulder 32 of the drive nut member 30′ by adding a radial component tothe pull up forces. The provision of the tapered outer wall 50 furthercan contribute to the radial component and stress distribution, as wellas controlled deformation of the rear ferrule 22′ during pull up. Inaccordance with the embodiments of FIGS. 15-20, the rear ferrule isprovided with a contoured drive surface that further reduces stressconcentrations in the area of engagement between the drive nut member30′ and the rear ferrule 22′.

[0062]FIG. 21 illustrates in an exemplary manner typical pull up stressdistributions at shoulder 32 and the rear ferrule drive surface 28′,typical in cases that incorporate a recess 40 type structure in the rearferrule as described herein before. These stress concentrations arerepresented by the arrows 200. By comparing the stress distributions ofFIG. 21 and the stress concentrations in FIG. 7 (FIG. 7 beingillustrative of a rear ferrule that does not include a recess-type ornotch structure 40) it is apparent that the provision of the recess 40concept significantly and substantially reduces stress concentration onshoulder 32 as noted hereinbefore. This reduction in stressconcentrations is further evident from a comparison of FIG. 7 with FIGS.9, 11 and 13.

[0063] Although FIG. 21 is not an FEA representation, it illustrates thepoint that the use of the recess 40 may not in all cases entirelyeliminate stress concentrations at the rear surface of the rear ferrule(albeit the use of the recess or notch 40 greatly reduces stressconcentrations in comparison to a rear ferrule that does not include anotch or recess). In the simplified representation of FIG. 21, stressconcentrations may exist for example at the radially inner and outerportions of the rear ferrule flange 26 (referred to herein as bi-modalstress concentrations as they can occur though not have to occur as tworegions of stress concentrations). These somewhat higher bi-modal stressconcentrations are represented by the heavier arrows in FIG. 21. Thepresent invention is thus directed to further reducing such stressconcentrations, with the results illustrated in FIG. 19, wherein thearrows represent a substantial elimination of pull up forceconcentrations using a modified rear ferrule drive surface and therecessed inner radius.

[0064] In accordance with this further aspect of the invention a twoferrule fitting is shown having a rear ferrule which is modified so asto reduce further the pull up stress concentrations by substantiallydistributing the stress concentration along the rear surface thatengages nut shoulder 32 of the drive nut member 30. As is shown in FIGS.15-18, corresponding fitting components are shown in finger-tightposition preparatory to final tightening.

[0065] With specific reference to FIGS. 15 and 16, the fitting comprisesa body 110 having a cylindrical opening 112 for receiving a tube end 113that bottoms on a counterbore 112 a. A tapered, frusto-conical cam mouth114 is located at the axial rear or receiving end of the opening 112. Afront ferrule 116 having a smooth, cylindrical, radially inner wall 118is closely received on tube end 113. The front ferrule 116 has a taperedouter surface 120 which engages tapered cam mouth 114 of the body 110.

[0066] Associated with the front ferrule 116 and located axiallyadjacent (i.e., in a rearward direction concentrically aligned with thelongitudinal axis of the fitting) is a rear ferrule 122 configured witha tapered nose portion 124 having a rearward tapered surface 127. Therear ferrule 122 also includes a radially extending rear flange 126having a contoured end face 128. The contoured face 128 includes arearward-facing driven surface 129 which is engaged by a respectivedriving surface 132 of the drive nut member 130.

[0067] The rearward tapered surface 127 of the rear ferrule 122 engagesand may have, but not necessarily, substantially the same angle as atapered cam surface 125 in the rear area of the front ferrule 116. Thenose portion 124 is joined with the rear flange 126 by a preferablytapered outer wall 131. In the illustrated embodiment the outer wall 131tapers with an increasing radial dimension in the axially rearwarddirection. The outer wall 131 could also be cylindrical, although it ispreferred to be tapered to further facilitate reduction of stressconcentrations on the driven surface 129.

[0068] The ferrules 116 and 122 are enclosed by a threaded drive nutmember 130 which includes a drive surface 132 that engages the drivensurface 129 of the rear ferrule 122. The drive nut member 130 threadablyengages a threaded portion of the body 110. During tightening andmake-up of the fitting, the drive surface 132 of the drive nut member130 applies pull up forces against the driven surface 129 of the rearferrule 122 to drive both ferrules axially forward (to the right asviewed in FIG. 16) into the fully engaged position shown in FIG. 19. Therear ferrule is configured so that upon forced engagement with thetapered cam surface 125, the nose portion 124 deforms radially inward.This action is desirable since it results in a tight gripping engagementof the rear ferrule 122 inner cylindrical wall with the outer surface ofthe wall of the tubing 113.

[0069] In the embodiments illustrated in FIGS. 15-20, the contoured endface 128 of the rear ferrule 122 may be rounded, curved, arcuate, orbowed or other curvilinear shape or combination of such shapes.Preferably but not necessarily the contoured end face 128 has a portionof which is a contour in the form of a convex radius R. The center ofthe radius can be, for example, internal to the ferrule body as shown inFIG. 18. However, those skilled in the art will readily appreciate thatthe origin of the driven surface 129 can be located anywhere withrespect to the rear ferrule structure with the illustration of FIG. 18being provided for illustrative purposes only. One aspect of thecontoured end face 128 is that with the driven surface 129 in the formof a convex radius, a line contact 129 b (or reduced face to face radialcontact) is formed initially with the nut drive surface 132, in a regionbetween the inner and outer radial portions of the rear flange 126. Therear ferrule also preferably includes a recess 140 which can be of anyconfiguration as previously described herein above. Alternatively, thecontoured end face 128 can be used with a rear ferrule configurationthat omits the recess 140, as illustrated in FIG. 20.

[0070] Although the use of a radius or other curvilinear surface for thecontoured end surface 128 is desirable, there is a practical limit as tohow small that radius can be made. If the radius of curvature is madetoo small then there will possibly be undesired stress concentrationsdevelop in the center region of the contoured end face 128.

[0071] A distinct advantage of the contoured rear ferrule 122 is thatpull up stresses between the nut drive surface 132 and the contoured endface 128 of the rear ferrule 122 are more uniformly distributed acrossthe contoured end face 128 of the rear ferrule, thus reducing andsubstantially eliminating stress concentrations. This further reductionof stress concentrations on the drive nut member 130 reduces pull uptorque and reduces galling, thus facilitating re-make of the fitting.

[0072] It is important to note that although the illustrated embodimentsshow an initial contact between the rear ferrule 122 and the drive nutmember 130 as generally in the middle of the contoured end face 128,this is not required in every application. The initial point of contactwill be a function of the overall fitting design, including the geometryof the tapered outer wall 131, the recess 140, the rearward taperedsurface 127, the front ferrule 116 configuration and so forth. But inkeeping with a general aspect of the invention, the contoured end face128 will be convex or axially variant in the region between the radialinner and outer portions of the rear flange 126 so as to distribute moreuniformly the pull up forces acting on the drive nut surface 132 toreduce galling and pull up torque as compared to a conventional rearferrule design that has a substantially flat non-contoured drivensurface.

[0073]FIG. 20 illustrates an embodiment of the invention in which therear ferrule 122′ has a substantially cylindrical inner wall 150′, butotherwise includes the rear flange 126′ having a contoured drivensurface 128′ and a nose portion 124′ with a rearward tapered surface127′ and a tapered outer wall 131′.

[0074]FIG. 22 illustrates another embodiment of the invention whereinthe rear ferrule 22′ design can have the recess 40′ shifted axiallyrearward, generally within the axial dimension of the rear flange 26.

[0075] With reference to FIGS. 23A-F, we illustrate a number ofvariations of the contoured end face 128. In FIG. 23A the contoured endface 128 is formed with an elliptical profile. In FIG. 23B, thecontoured end face 128 is formed by a blending of multiple radiuses suchas sections 128 a, 128 b and 128 c (dots on the drawing designate pointsof intersection of the arcs and not physical features of the end face).In FIG. 23C, the end face 128 includes a central portion 128 a having afirst radius profile, and outer portion 128 b formed by a second radiusprofile. In FIG. 23D the end face 128 includes a central portion 128 ahaving a profile formed by a radius and outer portions 128 b and 128 cformed as straight surfaces (in section the surface appears straight,though realized in the form of a conical surface). In FIG. 23E thecontoured end face 128 includes an elliptical central portion 128 a anda straight outer portion 128 b. And in FIG. 23F the contoured end face128 has a profile formed by three geometric shapes, an ellipticalcentral portion 128 a, a straight outer portion 128 b and a radiusedcenter portion 128 c. In all the examples of FIGS. 23A-F the point madeis that the selected profile and geometry for the contoured end face128, as with the earlier embodiments described hereinbefore, is designedto achieve the desired plastic deformation of the rear ferrule 122hinge-like nose to achieve excellent gripping of the tube while alsomaintaining the proper sequential pull-up operation with the frontferrule.

[0076] With reference to FIGS. 24A-F, the present invention can also berealized by incorporating a contoured profile in the nut drive surface132. In these embodiments, the contoured end face 128 is conical.Alternatively, both the nut drive surface 132 and the contoured end face128 could be contoured. FIGS. 24A-F correspond to FIGS. 23A-F as to thecontour shape applied to the nut drive surface 132. Thus, FIG. 24Aillustrates an elliptical profile; FIG. 24B illustrates a multiplecircle profile; FIG. 24C illustrates a two radius surfaces; FIG. 24Dillustrates a radius surface and two straight portions; FIG. 24Eillustrates an ellipse contour with a straight portion; and FIG. 24Fillustrates a combination of a radius, straight and ellipse portions. Inyet another embodiment of FIG. 24G, the nut drive surface 132 can beformed of two straight portions that join at an apex 129D.

[0077] With reference to FIG. 25, in still a further embodiment, therear ferrule 522 include a recess 540 in the inner cylindrical wall.However, in this embodiment, the rear flat portion 542 is formed by alarger diameter bore in the ferrule 522 body as compared to the diameterof the bore that forms the forward flat portion 544. By forming the rearflat portion 542 with a larger diameter, a single tool can be used toform the recess 540 and the central bores through the ferrule 522 body.The difference in the two diameters is represented by the dimension D inFIG. 25. Note that recess 540 is positioned in the rearward portion ofthe ferrule 522 body. This provides an axially elongated flat portion544 that assists in maintaining the ferrule in alignment during assemblysince the rear flat portion 542 does not as closely surround the tube.Those skilled in the art will readily appreciate, however, that theenlarged diameter rear flat portion 542 can be used with many of therecess profiles illustrated herein and others, including multiple notchdesigns. The rear ferrule 522 may also include a contoured rear wall asin the embodiments described herein.

[0078]FIG. 26 illustrates another embodiment of the rear ferrule 22′. Inthis embodiment, in addition to the double recesses 40′ in the centralthrough bore, the ferrule includes a recess 300 in the outer diametersurface 50′ of the ferrule. This recess 300 can be used as part of the‘hinge’ design to further control the plastic deformation of the ferrulenose portion 52′ during pull-up. FIG. 27 illustrates a further exampleof a rear ferrule 622 that incorporates the central recess 640, atapered outer diameter 650 having an outer diameter recess 300′, and thelarger diameter rear portion or radial flange 642 with a contoured orradius driven surface 628. The radial flange 642 is of a slightly largerdiameter than the forward surface 644, as in other examples herein, asrepresented by the dimension DD″ All of the actual dimensions andprofiles may be selected to cause the ferrule 622 to plastically deformwith desired loads against the tube surface and minimized loadconcentrations against the nut drive surface and also assure properdriving force into the front ferrule. As with the various other rearferrule designs illustrated herein, the various concepts of the rearferrule design can be used in a single ferrule fitting.

[0079] The ferrule illustrated in FIG. 27 includes the outer notch 300′.The FEA illustration of FIG. 28 dramatically shows how this outer notch300′ produces a significant hinge effect at the nose portion 652 of therear ferrule. The outer notch 300′ is bounded by a radially extendingcrown 302. This crown 302 functions to prevent the nose of the rearferrule 22 from slipping (as, for example, in a telescoping manner)under the front ferrule when the tubing is thin walled or otherwiseeasily deformed during make-up of the fitting. Without the crown 302, asthe thin tube wall collapsed the nose of the rear ferrule could beforced out of the camming mouth of the front ferrule and slip under thefront ferrule, preventing proper sequential pull-up and poor gripping byeither ferrule. Preferably, the crown 302 maintains contact with theinner camming mouth of the front ferrule during pull-up.

[0080] The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

1. A tube fitting, comprising: a fitting body having a cylindrical borefor receiving a tube end and including a tapered mouth at one end ofsaid bore that forms a camming surface; a drive member joinable withsaid body and having a ferrule drive surface; and a ferrule having atapered nose portion that extends into said tapered mouth of the fittingbody, a substantially continuous cylindrical interior wall that closelysurrounds the tube end, and a driven surface on a back end thereof thatengages said ferrule drive surface; said ferrule being case hardenedabout its entire surface, said ferrule having a rear portion of saidcylindrical interior wall that is radially spaced from the tube end uponpull-up of the fitting, a forward edge of said tapered nose portion thatpenetrates an outer surface of the tube end, and a collet portion ofsaid substantially continuous cylindrical interior wall that is axiallybehind said forward edge and that upon pull-up of the fitting isdeformed radially against said outer surface of the tube end to colletthe tube end.
 2. The fitting of claim 1 wherein said ferrule is deformedduring pull-up of the fitting by a toggle-like hinging action.
 3. Thefitting of claim 2 wherein said toggle-like hinging action results fromsaid rear portion moving radially outward from said outer surface of thetube end about a region of said ferrule that joins said rear portion tosaid collet portion.
 4. The fitting of claim 3 wherein said toggle-likehinging action causes said collet portion to be radially compressedagainst said outer surface of the tube end with a high gripping pressureupon pull-up of the fitting.
 5. The fitting of claim 3 wherein saiddrive member ferrule drive surface initially contacts said ferruledriven surface at a location radially outward to at least a centralportion of said ferrule driven surface.
 6. The fitting of claim 1wherein said driven surface is convex.
 7. The fitting of claim 1 whereinsaid convex surface is curved.
 8. The fitting of claim 1 wherein saidferrule comprises metal.
 9. The fitting of claim 8 wherein said metalcomprises stainless steel.
 10. A tube fitting, comprising: a fittingbody having a cylindrical bore for receiving a tube end and including atapered mouth at one end of said bore that forms a camming surface; adrive member joinable with said body and having a ferrule drive surface;a ferrule having a substantially continuous cylindrical interior wallthat closely surrounds the tube end, a tapered nose portion that extendsinto said tapered mouth, and a driven surface on a back end thereof thatengages said ferrule drive surface; said ferrule having a rear portionof said cylindrical interior wall that is radially spaced from the tubeend upon pull-up of the fitting, a forward edge of said tapered noseportion that penetrates an outer surface of the tube end, and a colletportion of said substantially continuous cylindrical interior wall thatis axially behind said forward edge and that upon pull-up of the fittingis deformed by a toggle-like hinging action that results from said rearportion moving radially outward from said outer surface of the tube endabout a region of said ferrule that joins said rear portion to saidcollet portion.
 11. The tube fitting of claim 10 wherein said colletportion is radially compressed against said outer surface of the tubeend to collet the tube end with a high radial gripping pressure.
 12. Thetube fitting of claim 10 wherein said ferrule is case hardened about itsentire surface.
 13. The fitting of claim 10 wherein said drive memberferrule drive surface initially contacts said ferrule driven surface ata location radially outward to at least a central portion of saidferrule driven surface.
 14. The fitting of claim 10 wherein said ferrulecomprises metal.
 15. The fitting of claim 10 wherein said metalcomprises stainless steel.
 16. A tube fitting, comprising: a fittingbody having a cylindrical bore for receiving a tube end and including atapered mouth at one end of said bore that forms a camming surface; adrive member having a threaded engagement with said body and having aferrule drive surface; a ferrule having substantially continuouscylindrical interior wall that closely surrounds the tube end, a taperednose portion that extends into said tapered mouth, and a driven surfaceon a back end thereof that engages said ferrule drive surface; saidferrule driven surface having a generally convex contour, a forward edgeof said tapered nose portion that penetrates an outer surface of thetube end, and a portion of said substantially continuous cylindricalinterior wall that is radially compressed by a toggle-like hingingaction to collet the tube end near said forward edge.
 17. The tubefitting of claim 16 wherein said ferrule is case hardened over itsentire surface.
 18. The tube fitting of claim 16 wherein said ferrulehas a rear portion of said cylindrical interior wall that is radiallyspaced from the tube end upon pull-up of the fitting.
 19. The fitting ofclaim 16 wherein said ferrule comprises metal.
 20. The fitting of claim16 wherein said metal comprises stainless steel.
 21. A tube fitting,comprising: a fitting body having a cylindrical bore for receiving atube end and including a tapered mouth at one end of said bore thatforms a camming surface; a drive member joinable with said body andhaving a ferrule drive surface; a ferrule having a substantiallycontinuous cylindrical interior wall that closely surrounds the tubeend, a tapered nose portion that extends into said tapered mouth, and adriven surface on a back end thereof that engages said ferrule drivesurface; said ferrule driven surface having a generally convex contour,a forward edge of said tapered nose portion that penetrates an outersurface of the tube end, a portion of said substantially continuouscylindrical interior wall that is radially compressed to collet the tubeend near said forward edge, and a rear portion of said cylindricalinterior wall that is radially spaced from the tube end upon pull-up ofthe fitting.
 22. The tube fitting of claim 21 wherein said ferrule iscase hardened over its entire surface.
 23. The fitting of claim 21wherein said ferrule is deformed during pull-up of the fitting by atoggle-like hinging action.
 24. The fitting of claim 23 wherein saidtoggle-like hinging action results from said rear portion movingradially outward from said outer surface of the tube end about a regionof said ferrule that joins said rear portion to said collet portion. 25.The tube fitting of claim 24 wherein said ferrule is case hardened overits entire surface.
 26. The fitting of claim 21 wherein said drivemember ferrule drive surface initially contacts said ferrule drivensurface at a location radially outward to at least a central portion ofsaid ferrule driven surface.
 27. The fitting of claim 21 wherein saidferrule interior cylindrical wall comprises a circumferential recessbetween said forward edge and said back end.
 28. The fitting of claim 21wherein said ferrule comprises metal.
 29. The fitting of claim 21wherein said metal comprises stainless steel.
 30. A method for sealingand gripping a tube end with a tube fitting of the type having a fittingbody and nut that are joinable and enclose a tube end, and a ferrulethat has a forward portion that engages the body and a rearward portionthat is driven by the nut when the fitting is pulled up, the methodcomprising the steps of: deforming the ferrule during pull-up of thefitting so as to cause a back end thereof to be radially spaced from thetube end upon pull-up; deforming the ferrule during pull-up so as tocause a front edge thereof to indent into the tube end; and deformingthe ferrule during pull-up with a toggle-like hinging action so that acollet portion thereof is radially compressed against the tube end. 31.The method of claim 30 wherein said collet portion is axially behindsaid indented front edge to isolate said indented front edge fromvibration.
 32. The method of claim 30 comprising the step of casehardening the ferrule over its entire surface prior to assembly into thefitting.
 33. The method of claim 30 comprising the step of forming acircumferential recess in a central bore of the ferrule prior toassembly into the fitting.
 34. The method of claim 30 comprising thestep of forming a convex driven surface at said back end of the ferruleprior to assembly into the fitting.
 35. A tube fitting comprising: afitting body having a cylindrical bore for receiving a tube end andincluding a tapered mouth at one end of said bore; a drive member havinga threaded engagement with said body and having a ferrule drive surface;a ferrule having a substantially continuous cylindrical interior wallthat closely surrounds the tube end when installed thereon, a taperednose portion that can be inserted into said tapered mouth, and a drivensurface on a back end thereof that engages said ferrule drive surfaceduring pull-up of the fitting; and wherein said ferrule is case hardenedabout its entire surface, and said ferrule has a configuration such thatupon pull-up of the fitting said ferrule will deform to cause: 1) a rearportion of said cylindrical interior wall to be radially spaced from thetube end, 2) a forward edge of said tapered nose portion to penetrate anouter surface of the tube end, and 3) a collet portion of saidsubstantially continuous cylindrical interior wall that is axiallybehind said forward edge to be deformed radially against said outersurface of the tube end to collet the tube end.
 36. A tube fittingcomprising: a fitting body having a cylindrical bore for receiving atube end and including a tapered mouth at one end of said bore; a drivemember having a threaded engagement with said body and having a ferruledrive surface; a ferrule having a substantially continuous cylindricalinterior wall that closely surrounds the tube end when installedthereon, a tapered nose portion that can be inserted into said taperedmouth, and a driven surface on a back end thereof that engages saidferrule drive surface during pull-up of the fitting; and wherein saidferrule is case hardened about its entire surface, and said ferrule hasa configuration such that upon pull-up of the fitting said ferrule willdeform with a toggle-like hinging action.
 37. The tube fitting of claim36 wherein during said toggle-like hinging action said ferrule willplastically deform so that: 1) a rear portion of said cylindricalinterior wall will be radially spaced from the tube end, 2) a forwardedge of said tapered nose portion will penetrate an outer surface of thetube end, and 3) a collet portion of said substantially continuouscylindrical interior wall that is axially behind said forward edge willbe deformed radially against said outer surface of the tube end tocollet the tube end